Logging-while-drilling Apparatus

Abstract

An improved logging-while-drilling apparatus comprising a drill collar having a logging-while-drilling tool therein. The tool has a turbinelike, rotary valve which opens and closes at a rate to generate a pressure wave signal in the drilling fluid representative of a measured downhole condition. The tool includes means to adjust the gap between the rotor and stator of the valve to thereby adjust the strength of the signal thus generated. A sleeve of wear resistant material is provided in the collar adjacent the valve to reduce erosion caused by the drilling fluid.

Description

Background of the Invention

The present invention relates to means for increasing the operational life of a logging-while-drilling tool and more particularly relates to a logging-while-drilling tool which includes means for adjusting the strength of the signal generated by the tool and means which compensates for certain wear caused by the erosive effects of the drilling fluid.

The desirability of a system which is able to measure downhole drilling parameters and/or formation characteristics and transmit them to the surface while actual drilling of an earth well is being carried out has long been recognized. Several such systems have been proposed and are commonly referred to as "logging-while-drilling" systems. In logging-while-drilling systems, one of the major problems exists in finding a means for telemetering the information from a downhole location to the surface and having it arrive in a meaningful condition.

In this regard, it has been proposed to telemeter the desired information by means of a pressure wave signal generated in and transmitted through the circulating mud system normally associated with rotary drilling operations. The pressure wave signal which is representative of a particular piece of desired information is generated in the mud downhole near the bit by a generating means or tool and the wave travels up the hole through the mud to a signal processor at the surface. One logging-while-drilling system utilizing this technique of telemetry is disclosed and fully described in U.S. Pat. No. 3,309,656 to John K. Godbey, issued Mar. 14, 1967.

In a logging-while-drilling tool of the type disclosed in U.S. Pat. No. 3,309,656, a turbinelike, rotary valve is positioned in the circulating mud path near the drill bit. A motor in the tool is energized in response to a measured piece of information to open and close the valve at a rate producing a pressure wave in the mud which is representative of said information. This pressure wave must have sufficient signal strength when it is generated for it to survive the inherent attenuation it undergoes in reaching the surface. Since attenuation is dependent on the distance the wave has to travel, signals from greater depths must be generated at greater strengths than those generated at lesser depths.

The turbinelike valve mentioned above is comprised of a stator and a rotor, each having openings therethrough which when aligned allow drilling mud to flow through the valve. When the openings are misaligned, flow therethrough is temporarily, partially blocked. The rate at which the valve opens and closes generates a defined pressure wave signal in the mud. The strength of the signal thus generated is dependent upon two important properties of the valve, these being "gap" and "bypass." Gap is defined as the distance between the bottom of the rotor and the top of the stator. Bypass is defined as that area between the outer circumferential perimeter of the rotor and the wall of the conduit in which the tool is positioned; the diameter of the stator of the valve being essentially equal to the inside diameter of the conduit.

Due to the position of the valve, the mud stream first passes through the openings in the rotor and then through the openings in the stator. It can be seen from the above definitions that the gap and the bypass of the valve determine the minimum area which is available for flow when the valve is in a closed position. It is this minimum area which inherently determines the strength of the generated signal.

It would be desirable to maintain both gap and bypass at a minimum in order to generate a signal having maximum strength regardless of what depth the tool is operating. However, other factors are present which have to be considered in order to provide a logging-while-drilling tool having an operational life sufficient to find widespread application in drilling operations. One such factor involves the peak torque loads which are imposed on the valve as it continuously rotates between its open and closed positions. These opposing torque loads increase substantially as the gap decreases so if the gap becomes too small, vibrations caused by these torques become critical. Also, due to the erosive nature of the drilling fluid and the extreme pressures involved, the operational life of the valve, itself, is adversely affected as the gap decreases.

It follows that in order to reduce unwanted vibrations and to increase the operational life of the valve, the gap should be enlarged to a maximum value but one which is still capable of generating a signal of desired strength. However, to enlarge the gap and still maintain the necessary minimum area, the bypass must be decreased. As the bypass decreases, serious erosion of the conduit wall adjacent the bypass normally takes place. This erosion of the conduit wall effectively increases the bypass which, in turn, decreases the strength of the signal being generated by the valve.

Therefore, to improve the operational life of such logging-while-drilling tools, means should be provided in the tool for protecting vulnerable areas of the valve and the conduit from excessive erosion. Also, means should be provided to adjust the gap of the valve to further compensate for certain erosive wear of the valve and the conduit so that desired signal strength may be maintained throughout the operational life of the tool.

Summary of the Invention

The present invention provides an improved logging-while-drilling apparatus of the type described above which includes a means for adjusting the gap between the rotor and stator of the signaling valve thereof so that wear to critical areas of said apparatus can be compensated for to maintain a desired signal strength. Further, the present invention includes the provision of wear resistant material to exposed areas of the apparatus to extend the operational life thereof.

Structurally, the logging-while-drilling apparatus comprises a drill collar which is adapted to be connected into and form a portion of a drill string of an earth drilling apparatus. A logging-while-drilling tool having a housing is positioned in the collar. A turbinelike, rotary valve is carried by the housing and is positioned so that at least a portion of the drilling fluid flowing through the drill string will flow through said valve. The valve is comprised of a rotor and a stator. The rotor is affixed to a shaft extending from the housing and is rotated thereby at a speed determined by a measured downhole condition. The stator is affixed to the housing. In one embodiment, the stator is threaded on the housing so that the stator may be moved along the longitudinal axis of the housing to adjust the gap between the rotor and the stator. In another embodiment, means are provided where the rotor may be moved along the longitudinal axis of the shaft to adjust said gap.

A sleeve of wear resistant material is provided within the collar adjacent the valve to resist erosion caused by the drilling mud and to thereby extend the operational life of the logging-while-drilling apparatus. By reducing erosion of the collar wall adjacent the valve, the inherent increase in the bypass between the rotor and wall is retarded. Further, wear resistant material is provided for those surfaces of the valve which are exposed to erosive effects of the drilling fluid.

BRIEF DESCRIPTION OF THE DRAWINGS

The actual construction, operation, and the apparent advantages of the invention will be better understood by referring to the drawings in which like numerals identify like parts and in which:

FIG. 1 is a schematic elevation of a rotary drilling apparatus including in vertical section a well containing a drill string in which the present invention is employed;

FIG. 2 is a schematic elevation, partly in section, of a portion of the drill string of FIG. 1, having a logging-while-drilling tool mounted therein which utilizes the present invention;

FIG. 3. is a detailed sectional view of one modification of the upper portion of FIG. 2 illustrating one embodiment of the present invention;

FIG. 4 is a detailed sectional view of another modification of the upper portion of FIG. 2 illustrating another embodiment of the present invention; and

FIG. 5 is a sectional view taken along section line 5--5 of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring more particularly to the drawings, FIG. 1 discloses the present invention as used in a logging-while-drilling system which is incorporated in a rotary drilling apparatus. A derrick 21 is disposed over a well 22 being formed in the earth 23 by rotary drilling. A drill string 24 is suspended within the well and has a drill bit 27 at its lower end and a kelly 28 at its upper end. A rotary table 29 cooperates with kelly 28 to rotate string 24 and bit 27. A swivel 33 is attached to the upper end of kelly 28 which in turn is supported by hook 32 from a traveling block (not shown). This arrangement not only supports the drill string 24 in an operable position within well 22 but also forms a rotary connection between the source of circulating drilling fluid, such as mud, and the drill string 24. It should be understood that "mud" as used throughout this disclosure is intended to cover those fluids normally used in rotary drilling operations.

The pump 36 transfers drilling mud from a source, such as pit 34, through desurger 37 into mudline 38. Desurger 37 is adapted to reduce the pulsating effect of pump 36 as is well known in the art. The mud flows through mudline 38, flexible hose 39, swivel 33, drill string 24, and exits through openings (not shown) in drill bit 27 to pass outwardly into well 22. The mud then circulates upward carrying drill cuttings with it through the annulus between the well and drill string 24 to the surface of the earth 23. At the surface, well head 41 is secured to casing 40 which is cemented in the well 22. Pipe 42 is connected to casing 40 for returning the mud to pit 34.

As schematically illustrated in FIGS. 1 and 2, a logging-while-drilling tool 46 is located in drill collar 26 which forms a part of the lower end of drill string 24 near bit 27. Tool 46 has a motor-actuated rotary valve which periodically interrupts at least a portion of the drilling fluid flowing through the valve to thereby generate a pressure wave in the fluid which is representative of a measured downhole condition. This is the type of logging-while-drilling tool which is disclosed and described in U.S. Pat. No. 3,309,656 to John K. Godbey. The present invention is directed to improving the operational life and performance of the valve. However, in order to fully understand and appreciate the present invention, a brief description of the entire tool 46 will be helpful.

A transducer means which is capable of measuring a desired downhole condition and converting the measurement to an electrical signal is positioned downhole on or near tool 46. As illustrated, transducer means 54, e.g., a strain gauge, is positioned on drill collar 26 to measure the downhole weight on bit 27. The signal from transducer means 54 is applied to electronic package 53 which is sealed in compartment 48 of tool housing 46a. For an example of such an electronic package, see U.S. Pat. No. 3,309,656. Circuitry in package 53, in response to the signal from means 54, allows a defined amount of power from electric power generator 50 in compartment 49 of housing 46a to flow to the variable speed, electric motor 55 in compartment 47 of housing 46a. A turbine 52 driven by the mud flow rotates generator 50 to produce electrical power. Motor 55, in response to the amount of electricity passing through package 53, will drive rotor 61 of signal generating valve 60 through gear train 56 at the rotational speed necessary to generate a pressure wave signal in the mud which is representative of the measured condition.

Referring now to the more detailed representation in FIG. 3, signal generating valve 60 is comprised of a rotor 61 and a stator 62. Rotor 61 is fixed on shaft 63 of gear train 56 by means of tapered bushing 64 and nut 65. Shaft 63 is journaled in housing 46a by means of bearings 66. Seal 67 around shaft 63 seals the interior of housing 46a against the influx of drill mud. Preferably, both rotor 61 and stator 62 contain the same number of identical spaced opening or slots, 61a, 62a, respectively (FIG. 5), each of the slots being of substantially the same area. Value 60 is in an open position when the slots are aligned and is in a closed position when the slots are completely misaligned. When valve 60 is in a closed position, the only flow through the valve is that which passes through gap 70 and bypass 71. Gap 70, as can best be seen in FIG. 3, is that distance between the bottom surface of rotor 61 and the top surface of stator 62. Bypass 71 (FIGS. 3 and 5) is that distance between the outer periphery of rotor 61 and the wall of the conduit adjacent the rotor. The outer diameter of stator 62 is effectively the same as the interior diameter of the conduit.

The rate at which valve 60 opens and closes determines the frequency of the pressure wave signal thus generated in the drilling mud, but the strength of the signal is directly related to the minimum area as defined by gap 70 and bypass 71 which is available for flow when the valve is closed. As this area decreases, the signal strength increases. Since a strong signal is desired, this minimum area should be as small as possible. However, when gap 70 becomes too small, unwanted vibrations occur as valve 60 rotates between its open and closed position. These vibrations adversely affect the signal being generated by the valve. Further, severe erosion of rotor 61 and stator 62 normally takes place as gap 70 is reduced which in turn reduces the overall operational life of tool 46. Therefore, it becomes desirable to maintain gap 70 as large as possible and still maintain the minimum area necessary for the generation of a signal having sufficient strength to reach the surface from the depth at which tool 46 is operating.

In order to increase gap 70 and still maintain a desired minimum area, bypass 71 has to be decreased. When this is done, erosion of the wall of the drill collar 26 in which tool 46 is positioned may become critical in the area surrounding rotor 61. The present invention provides a means whereby gap 70 can be relatively large at shallow depths of drilling operations where the generated signals can be of lesser strength and then be decreased by adjustment for generating signals of greater strength as the drilling depths increase. Providing a relatively large gap at the shallower depth and decreasing the gap when it becomes necessary to increase signal strength substantially reduces the rate of erosion of the valve and accordingly extends the operational life of tool 46. Also, by making gap 70 adjustable, the gap can be decreased as normal wear inherently increases bypass 71.

In accordance with the present invention, one means for adjusting gap 70 is illustrated in FIG. 3. In this embodiment, stator 62 is threaded on its interior surface to mate with threads on housing 46a. It can been seen that stator 62 can be threaded towards or away from rotor 61 thereby adjusting gap 70 to its desired value. Set screw 75 is provided to lock stator 62 in its desired position. By means of the cooperating threads on stator 62 and housing 46a, gap 70 can be relatively large for operations at shallow depths and then decreased for operations at greater depths. This adjustment would normally be made while drill string 24 was removed from well 22 to change bit 27 as is well known in the art.

FIG. 4 discloses another embodiment of tool 46 having an alternative means for adjusting gap 70. In this embodiment, rotor 161 is made to be adjustable on shaft 163. Shaft 163 has a reduced integral portion 164 which extends from its upper end into internally threaded recess 165 on rotor 161. Spacer 166 having a smooth bore is positioned for free movement relative to portion 164 but is threaded on its outer surface to cooperate with the threads in recess 165. It can be seen that the position of spacer 166 within recess 165 will determine how far rotor 161 will receive shaft 163 and will thereby determine gap 70. Locking nuts 167, 168, and protective cap 169 secure rotor 161 on shaft 163 in its desired position for rotation therewith.

As stated above, when gap 70 is reduced, erosion of the conduit wall adjacent valve 60 becomes a problem. If unchecked, this erosion inherently increases bypass 71 so that the minimum area defined by bypass 71 and set gap 70 will increase, thereby effectively reducing the strength of the signal being generated by valve 60. Further, this erosion can ruin the relatively expensive drill collar 26 to the extent that the entire collar will need to be replaced during drilling operations.

In accordance with the present invention, sleeve 80 of ware resistant material is positioned in the bore of collar 26 adjacent valve 60. This material is one which exhibits substantially greater resistance to wear than that exhibited by collar 26 so that the operational life of tool 46 is extended. An example of a wear resistant material which exhibits a relatively long life, e.g., 100 hours or more under normal operating conditions of valve 60, is one having 45 percent titanium carbide particles in a tool steel matrix and is commercially available under the trade name "Ferro-Tic." By replacing only sleeve 80 when it becomes unduly worn, a single collar 26 can be used throughout normal drilling operations.

Since wear also occurs to the exposed surfaces of both rotor 61 and stator 62, it is desirable to protect these surfaces with wear resistant material. For example, caps of wear resistant material, e.g., Ferro-Tic, may be screwed or otherwise secured to the exposed surfaces of the rotor and stator to substantially extend the operational life of valve 60.

Claims

What is claimed is:

1. A logging-while-drilling tool comprising:

a housing adapted to be positioned in a drill string of an earth drilling apparatus wherein a drilling fluid which is circulated through the drill string will flow around said housing;

a rotary valve positioned on said housing so that at least a portion of the drilling fluid flowing through the drill string will flow through said valve whereby a pressure wave signal will be generated in the drilling fluid as said valve opens and closes in response to a downhole condition measured by said tool, said valve comprising:

a rotor having openings therethrough mounted on a shaft extending from said housing;

a stator on said housing having openings therethrough which when aligned with said openings in said rotor allow flow through said valve and when misaligned effectively block flow through said openings in said rotor; and

means for adjusting the gap between said rotor and said stator.

2. The logging-while-drilling tool of claim 1 wherein said means for adjusting said gap comprises:

cooperating means on said shaft and said rotor for affixing said rotor to said shaft at different positions along the longitudinal axis of said shaft.

3. The logging-while-drilling tool of claim 1 wherein said means for adjusting said gap comprises:

cooperating means on said stator and said housing for affixing said stator to said housing at different positions along the longitudinal axis of said housing.

4. The logging-while-drilling tool of claim 3 wherein said cooperating means comprises:

mating threads on said stator and said housing.

5. A logging-while-drilling apparatus comprising:

a conduit adapted to be connected into a drill string of an earth drilling apparatus;

a logging-while-drilling tool positioned within said conduit, said tool comprising:

a housing;

a rotary valve on said housing positioned so that at least a portion of any drilling fluid flowing through the drill string will flow therethrough, said valve comprising:

a rotor having openings therethrough mounted on a shaft extending from said housing;

a stator on said housing having openings therethrough which when aligned with said openings in said rotor allow flow through said valve and when misaligned effectively block flow through said openings in said rotor;

means for adjusting the gap between said rotor and said stator; and

wear resistant means on the wall of said conduit at least along that portion which is adjacent said valve.

6. The logging-while-drilling apparatus of claim 5 wherein said wear resistant means comprises:

a sleeve of material having a resistance to wear greater than that of the conduit wall.

7. The logging-while-drilling apparatus of claim 6 wherein:

said wear resistant material is comprised of titanium carbide particles in a tool steel matrix.

8. The logging-while-drilling apparatus of claim 6 wherein said means for adjusting said gap comprises:

cooperating means on said shaft and said rotor for affixing said rotor to said shaft at different positions along the longitudinal axis of said shaft.

9. The logging-while-drilling apparatus of claim 6 wherein said means for adjusting said gap comprises:

cooperating means on said stator and said housing for affixing said stator to said housing at different positions along the longitudinal axis of said housing.

10. The logging-while-drilling apparatus of claim 9 wherein said cooperating means comprises:

mating threads on said stator and said housing.

11. The logging-while-drilling apparatus of claim 10 wherein:

those surfaces of said valve which are exposed to drilling fluid are covered with wear resistant material.